The present disclosure relates to a method of forming a semiconductor structure, and more particularly to a method of forming a semiconductor structure including a transferred semiconductor layer, and structures for effecting the same and formed by the same.
A substrate including a thin silicon layer can be formed by employing a hydrogen-containing cleavage layer. For example, hydrogen ions (protons) can be implanted into a bulk silicon substrate to form a hydrogen-containing layer at a constant depth from a top surface of the bulk silicon substrate. A handle substrate is bonded to the top surface of the bulk silicon substrate, and the bulk silicon substrate is subsequently cleaved at the hydrogen-containing layer so that a thin silicon layer above the hydrogen-containing layer is “transferred” to the handle substrate to form a new substrate, which is an assembly of the handle substrate and the transferred thin silicon layer. The remaining portion of the bulk substrate is planarized by chemical mechanical planarization and re-used to provide another thin silicon layer for another layer transfer process until the thickness of the bulk substrate becomes too thin to be employed for layer transfer purposes.
The method of forming a substrate including a thin silicon layer employing hydrogen implantation is subject to many limitations. First, a hydrogen-containing layer must be formed through hydrogen implantation. Because of inherent depth distribution of the implanted hydrogen ions, a high dose of hydrogen ions must be implanted into the bulk silicon substrate to be able to induce cleavage at the hydrogen-containing layer. Because the vertical distribution range of the hydrogen ions increases with increasing depth of implantation, higher dose of hydrogen ions is needed as the depth of the hydrogen-containing layer increases.
Further, due to the propensity of bulk silicon substrates to cleave along major crystallographic planes, cleavage along only some crystallographic orientations of a silicon crystal produces clean cleavage planes with atomic planarity, while cleavage along other crystallographic orientations can produce cleavage planes that include facets and/or rough surfaces that need to be planarized, for example, by chemical mechanical planarization.
Yet further, the bulk substrate after cleavage needs to be planarized before re-usage. In addition, any modification to the dopant concentration in the transferred layer requires additional processes that include implantation or plasma treatment and dopant activation by a high temperature anneal.
Thus, a process of forming a transferred silicon layer without employing hydrogen ion implantation is desired.